Balanced Rotisserie

Started by skmini, January 21, 2022, 07:06:46 AM

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skmini

rolloverjigs.com sells a rotisserie for the Mini that does not involve a tube going through the middle of the Mini; it attaches where the front subframe does and across the shock towers and parcel shelf in the rear.  In a thread on theminiforum where someone was complaining about how difficult the Mini is to turn on the rotisserie, someone else commented that if you have it balanced correctly, it's easy to turn and the balance point is about 16" up from the floor.

I've got a Mk4 Mini without the cutout in the rear seat back and I wasn't keen on cutting a hole there.  Seeing all the schemes for locking the rotation of the Mini and various levers and hydraulic jacks for rotating it, something that was better balanced sounded good to me, so I built one using the rolloverjigs.com one as inspiration.  The result is a rotisserie that has no method of locking the shell in place; it's balanced well enough and there's enough friction in the pivots that I can easily rotate it and it will stay in place for most things I need to do.

A couple of things I kept in mind:
1.  The center of gravity of a saloon shell without doors, bootlid or hood is 16" up from the floor.
2.  A 5/8 bolt fits nicely in 1/2" black pipe and makes a nice hinge/pivot of any length you would like.

Materials I used:

34' of 1x2 tube
8' of 1.5" tube (just what I had on hand, could/should have used 1x2 or 1x1 tube for this)
12' of 2" angle
31' of 1" tube
4' of 1.5" angle
8" of 1/2" black pipe
4 5/8-11 6" bolts, matching lock nuts and flat washers
4 casters
10 2" long 3/8" bolts and nuts for bolting to the steering rack mount, rear parcel shelf, and joining the pieces of the rear attachment.
2 3.5" long 3/8" bolts for joining the pieces of the front attachment.
2 bolts for connecting the rear attachment to the shock towers.  Can't remember what I used for sizes here.

Plans:

I don't have any.  Something I enjoy with welding is how easy it is to fab things up on the fly, so I basically made this up as I went and built it in situ.  For the attachment points on the Mini, this probably isn't a bad idea.  For example, I was able to take advantage of some reinforcing brackets on the parcel shelf that may or may not exist on your Mini, and we all know no two Minis are exactly the same dimensions.  That being said, I did make a few sketches and calculations ahead of time to give me a rough idea of how I was going to build the stands everything sits on.  Needs to be at a height where I can rotate the shell without hitting the floor or the 8' ceiling.  I chose an equilateral 48" triangle, so the 1x2 tubes angling up towards the pivot are each 48" and so is the 1.5" square tube joining them at the bottom.  The rolloverjigs.com jig uses some bolts and brackets at the bottom so you can fold the stand up and make it easier to assemble without welding.  I welded everything together because I'm likely to only need the rotisserie for this car.  I'm planning to cut everything apart once I'm done and repurpose the steel for other projects.

skmini

#1
Building the rear attachment

For both the front and rear attachments, I wanted something that ended up level vertically and with some wiggle room to be able to move the pivot point up and down in case 16" didn't work.  I had the shell with its floor on a dolly, so the floor was level and it would be easy to measure 16" up from the floor.

1. a 41" 1x2 tube across the shock towers.
2. 2 24" 1x2 tubes welded 16" apart on the outside perpendicular to that tube towards the rear
3. a 41" 1" square tube across the parcel shelf, bolted to a handy reinforcement
4. 2 6" 1" square tube pieces welded to two 4" 2" angle pieces.  These were welded to the parcel shelf tube and bolted to the 2 24" 1x2 tubes.

I didn't worry about getting any of the above pieces level, just straight and at right angles.  Then, the pivot point attachments:

1. 2 16" 2" angle pieces welded to the 24" 1x2 tubes.  I made sure these were level vertically in both dimensions, and centered on 16" from the floor.  As it turns out, the two 24" 1x2 tubes are about 16" from the floor.
2. 2 16" 2" angle pieces joined with a 16.5" 1x2 tube.  I don't have a picture of this, but I built this by clamping the 2" angle pieces to the 2" angle pieces that were already welded to the rear attachment and then welded the 1x2 tube to them, centered and level.

While I had the 2" angle pieces clamped together, I drilled a couple of holes through for bolts to attach them to each other once the Mini was lifted on to the stands.

I also drilled a 5/8" hole through the middle of the 16.5" 1x2 tube for the pivot.

skmini

#2
Building the front attachment

1. 32" 1x2 tube across the top subframe mounts with a 4" piece of 1x2 underneath each subframe bolt and 6" 5/8-11 bolts used to bolt it in.  This may be different if you have a Mk1/2/3 body.
2. 2 26" 1x2 tube extending out the front welded to the 32" 1x2 tube 16" apart on the outside.
3. 2 16" 2" angle welded to the 2 26" 1x2 tube, level vertically and centered 16" from the floor of the Mini.

As you can see, the top of front crossmember is quite a bit higher than 16" from the floor, and at a bit of an angle.  The important thing is that the 2" angle is level vertically.  This will make it parallel to the equivalent 2" angle on the rear and make sure the pivot points are in line.

1. 2 16" 2" angle pieces with a 16.5" 1x2 tube welded in the middle for the pivot.  This was done the same way it was at the front by clamping the angle and 1x2 tube and then welding the 1x2 tube to the angle.  Note I've also drilled the 5/8" hole in the middle of the 1x2 tube, and drilled holes through the 2" angle for the bolts.
2. 2 25" 1" square tubes to tie into the steering rack mounts.  These are then bolted to the steering rack mounts and bolted to the two 26" 1x2 tubes.  I chose the steering rack mounts because the holes are in line vertically and happened to line up fairly well to the 1x2 tubes.

skmini

Building the stands

As mentioned in the beginning, these are 48" on a side.  I made each out of 2 48" pieces of 1x2 tubing and 1 48" piece of 1.5" square tubing, plus the black pipe and some angle to mount casters to.  The 1x2 tubing to 1.5" tubing is not pretty, and there are better ways to do this.  I also briefly considered using a threaded rod to tie the two pieces of 1x2 tubing together about mid-way up.  Then I could use the threaded rod to lift the Mini up and down, which would have made mounting the Mini on the rotisserie much easier.

1. I roughly "fish-mouthed" then ends of the 1x2 tubing and welded it to the 1/2" black pipe.  To keep the two 2" pieces of pipe in line, I welded the 1x2 tubing to a 4" piece of pipe after squaring it and clamping it, and then cut the pipe in half.
2. I welded a small piece of steel against the bolt head to keep it from turning.
3. I used a washer at the lock-nut to keep it from turning, but should have also put a washer between the 1/2" pipe and the 1x2 tubing that the bolt goes through.

skmini

Lifting the Mini onto the stands.

I don't have pictures for this.  If you look carefully in the pictures of the 2" angle pieces, you'll notice I drilled holes for bolts to bolt them together once the Mini is on the stands.  My procedure, made up as I went along:

1. Lift the rear of the Mini to the height of the stand, put the bolts through the holes and put the nuts on.  Just tilting the shell up like this fairly easy: I think I did it with a floor jack and a 2x4 across the heel board panel.  There was enough of an angle to the tilt that I could bolt the rear stand on.
2. Lift the front of the Mini to the height of the stand, put the bolts through the holes and put the nuts on.  This was a lot more difficult because now the shell was a lot higher.  I couldn't use my floor jack to lift the body.  I used a step-ladder and a 2x4.  "Give me a lever long enough and a fulcrum to place it..."  End of the 2x4 on the step ladder (fulcrum) beside the Mini, 2x4 (lever) underneath the two 1x2 tubes sticking out from the front of the Mini.  Lift the 2x4 to lift the Mini up to the stand, put the bolts through the holes.  A shop crane would probably also work here, although that probably depends on how you build the stand and whether the legs of the crane can go underneath it.

Once the Mini was up on the stands, I welded two pieces of 11' 3" of 1x1 tubing to join the front and rear and attached the casters.  Later, I added small 1x2 tubing braces between those 1x1 tubes and the 1x2 uprights to minimize racking.

cstudep

This is excellent! Thank you for taking the time to put this all together, it will come in very handy when I decide to tear mine down for the repaint. 4.gif

MiniDave

#6
And you're a pretty good welder too!

Seems like it's higher off the ground than it needs to be to be able to spin it all the way around?

Most of the ones I've seen or used just had a single pipe in the center, running between the two ends at the floor - do you find yourself stepping on or kicking those two connecting tubes?
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

skmini

It is a bit higher than it needs to be. I should take a measurement of the lowest point.

I haven't had a problem hitting or tripping over the connecting tubes.  They're 4' apart, and the shell is about 4' wide, so unless I'm working on the topside of the front fenders with the shell on its side, they're mainly under the shell.  I considered a single tube in the middle, but had a bunch of 1" tube.  I figured it would be a bit too flexible.

skmini

At its lowest point, the shell is 8" above the bottom of the stands, 12" above the floor with casters on the stands.
At its highest point, the shell is 16" from the 8' ceiling.

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